JP3704180B2 - Desulfurization method of low silicon concentration hot metal - Google Patents

Desulfurization method of low silicon concentration hot metal Download PDF

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JP3704180B2
JP3704180B2 JP14792995A JP14792995A JP3704180B2 JP 3704180 B2 JP3704180 B2 JP 3704180B2 JP 14792995 A JP14792995 A JP 14792995A JP 14792995 A JP14792995 A JP 14792995A JP 3704180 B2 JP3704180 B2 JP 3704180B2
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hot metal
desulfurization
cao
concentration
ash
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JPH093515A (en
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進 務川
義正 水上
拓男 三戸
充高 松尾
意智 國武
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Nippon Steel Corp
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Nippon Steel Corp
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【0001】
【産業上の利用分野】
本発明は、溶銑の高効率な脱硫処理方法に関するものであって、溶銑予備処理分野に広く利用される。
【0002】
【従来の技術】
鋼材中の硫黄は、硫化物系介在物生成により鋼材の特性を劣化させる性質を持つ。例えば、対サワー用鋼管などでは5ppm という低いレベルの硫黄濃度が要求されている。
【0003】
こうした要求に応えるために、鉄鋼精錬においては脱硫処理技術が発展してきた。脱硫処理のうち溶銑段階での処理は生石灰、あるいはカーバイド、ソーダ灰等、塩基性の高い酸化物や金属Mgなどを利用してCaS,Na2 S,MgS等の硫化物を生成させてスラグとして分離除去する方法が採られている。また、極低硫黄濃度を達成するためには粗精錬溶鋼を更にCaO系フラックスを用いて脱硫処理することも行われている。
【0004】
一般に、硫黄はNa,Mg,Ca等アルカリ金属あるいはアルカリ土類金属との結合力が高く、これらの元素と下式の通り反応し硫化物を生成させて除去しようとするのが脱硫処理である。これらのうちでもNa,Mg,Caの順でその結合力が高いが、工業的規模で安価で安定に供給し得る材料としてCaOを主成分とする生石灰や石灰石、Na2 CO3 主成分とするソーダ灰、あるいはCaC2 を主成分とするカルシウムカーバイト、金属Mgが用いられているわけである。これらのうち、Na系、Mg系に比べて硫黄との結合力は弱いもののCaOを主成分とする石灰系フラックスは資源量が豊富でかつ安価で取り扱いも容易なことから、鉄鋼精錬においては工業的に広く用いられている。
CaO+S→CaS+O ‥‥(1)
Na2 CO3 +S→Na2 S+CO2 +O ‥‥(2)
Mg+S→MgS ‥‥(3)
【0005】
一方、CaO自体は融点が2800℃と非常に高く、単に溶鉄と接触させても固体状態に留まる。この場合、脱硫反応は固体CaO内のSの固相拡散によって進行することになるが、この過程は一般に非常に遅いことが知られている。従って、固体CaOのままでは反応性に乏しいため、単体では脱硫速度が遅いという欠点を有する。そこで、通常はCaF2 等、滓化、溶融性を高め、反応性を上げるための副剤添加する、あるいはこれらと事前に焼成して融点を下げる等の工夫がなされている。
【0006】
他方、溶銑段階での脱硫処理は溶鋼段階での脱硫処理時に比べて低温であり、(1)式の反応が高温程右へ進み易いので温度の点で溶鋼での処理に比べて不利ではあるが、CaF2 等滓化助剤を添加すると溶鋼段階の方が著しく耐火物の損耗が進むこと、溶銑中に多量に含まれる炭素による溶鉄中の硫黄の活量上昇による利点もあり、積極的に溶銑脱硫処理が採用されている。
【0007】
【発明が解決しようとする課題】
溶銑脱硫において用いられる石灰系フラックスとしては、特公昭55−24925号公報、特公昭63−195208号公報に見られるように、CaOとAl2 3 を特定配合組成で混合溶融する旨の記述がある。これらの方法はその精錬上の改善効果は認められるものの、事前焼成を行うことは著しいエネルギーを要し、フラックスコスト高を招くために安価であるという生石灰系フラックスの特徴を逸脱するので、一部の高級鋼向けに二次精錬で使用されることはあっても、普通一般鋼へ広く適用出来ない方法である。
【0008】
また、特公平2−305913号公報には、生石灰に溶融滓化助剤としてAl2 3 を添加し、高温の溶銑に吹き付けることにより、フラックスを溶融させて硫反応を促進させる旨の記述がある。CaO−Al2 3 二元系の場合、混合比が重量で1:1の所で最も融点の低い組成となり、その融点は1400℃程度であることが知られている。しかし、この方法では溶銑側の温度に制約が生じる。例えば、溶銑予備脱りん後の1350℃前後の温度では使えないという問題がある。
【0009】
更に、特公平5−78723号公報にはCaO−Al2 3 系により滓化溶融性を向上させるためにSiO2 あるいはCaF2 を混合する旨の記述がある。SiO2 は珪石等の形で安価に多量に入手可能な副材として滓化剤として使い易いものの、スラグの脱硫能力を落とすものであるから、SiO2 を滓化助剤とすることは本来好ましくない。
鉄鋼精錬において工業的に用し得る副材料の中では生石灰の滓化を最も良く助け、かつスラグの脱硫能力を低下させないことが知られているものとしてCaF2 があるが、これは耐火物を著く浸食するので、例えば特に極低硫黄濃度が要求される一部の高級鋼向けに二次精錬においてCaOとCaF2 の混合フラックスが用いられているに過ぎない。
【0010】
一方、CaOを完全に滓化・溶融させるまでも無く、微粉として吹き込むことにより、固体生石灰中のSの拡散距離を短くし、脱硫速度が大きく出来ることは良く知られている。そのため、例えば、特公昭54−37020号公報には溶銑に吹き込むCaOの粒径を0.4mm以下とする旨の記述がある。一方、生石灰粒径があまり細かい飛散してしまう等ハンドリング上の問題が生じること、吹き込み用のホッパー、ブロータンク、配管内への付着が起き、操業が不可能となる等の問題があり、微粉化には自ずと工業的に利用出来る限界がある。
【0011】
他方、微粉を吹き込む場合においても、共存元素により脱硫効率が大きく影響を受けることが知られている。
例えば鉄と鋼vol.61(1975),p.29に記されているように、溶銑が珪素を含有する場合には、(1)式で生成する自由な酸素によって珪素が酸化され、生石灰表面に高融点酸化物である3CaO・SiO2 (融点:2150℃)、2CaO・SiO2 (融点:2180℃)が生成し、Sの生石灰粒内への拡散を阻害し脱硫速度を低下させることが知られている。これを避ける手段として特公昭56−23220号公報には、粉末AlをAl2 3 やCaOとともに溶銑に吹き込んで事前に溶銑中のAl濃度を調整して、更にCaO,CaC2 を吹き込んで脱硫する旨の記述がある。Alは酸素による珪素の酸化反応を抑制する目的で添加するとの記述があり、Al添加量を(4)式で規定している。
[%Al]=(0.01〜0.1)[%Si]+(0.2〜1.0)×Δ[%S]‥‥(4)
但し、[%Si]:溶銑中の珪素濃度(重量%)
Δ[%S]:狙いとする脱硫幅(重量%)
【0012】
更に特公昭55−110711号公報にはやはり珪素の酸化抑制の観点からAlをCaOと同に吹き込む旨の記述がある。
この点について本発明者らは本発明に至る詳細な研究により、Alを添加する場合には珪素濃度の低い溶銑で脱硫することが望ましいこと、このような条件下では非常に高い脱硫効率が得られることを明らかにしたが、珪素濃度の高い溶銑では、添加したAlの効果が最大限に発揮されないという問題があった。
【0013】
類似の技術として特公昭56−58912号公報にはカルシウムカーバイト20〜90%、生石灰75〜5%、およびAl残灰1〜5%とした脱硫剤の記述があるが、その組成についての技術的根拠は曖昧である。
【0014】
以上のような問題点があるため、石灰系フラックスによる溶銑脱硫処理は依然としてある程度微粉化した生石灰そのものを溶銑に吹き込む方法が広く行われているのが現状である。
このような状況に鑑み、本発明は安価で効率の高い溶銑の脱硫処理を可能とする石灰系脱硫剤を提供することを目的とするものである。
【0015】
【課題を解決するための手段】
本発明は、
(1)生石灰を主成分とするフラックスとAl灰の混合フラックスによる溶銑の脱硫処理に際し、脱硫剤中のCaOとAl2 3 の混合比がAl2 3 で33〜37.7重量%の範囲となるように混合したもの、または添加後のCaOとAl2 3 の混合比がAl2 3 で33〜37.7重量%の範囲となる量の生石灰、Al灰を添加することを特徴とする低珪素濃度溶銑の脱硫方法。
(2)原料の粒度が22mesh以下の粉体から成るフラックスを吹き込む前項(1)記載の溶銑の脱硫剤である。
【0016】
【作用】
金属Alが存在する場合、脱硫反応は次式で表される。
【0017】
3CaO(固体)+3S+2Al=3CaS(固体)+Al2 3 (固体)‥‥(5)
この反応の平衡定数を用いると平衡到達硫黄濃度は(6)式のように、スラグ側のCaO,Al2 3 ,CaSの活量aCaO ,aAl2 O 3 ,aCaS 、溶銑中のAl濃度を用いて表される。
平衡到達[%S]={(aCaS aAl2 O 3 )/(KaCaO [%Al]2 )}1/3 ‥‥(6)
【0018】
本実験条件の1350℃ではスラグは固体状態であるため、固体スラグと溶銑間の反応を考慮すれば良い。即ち、同一CaO−Al2 3 の比率であれば平衡硫黄濃度は溶銑中のAl濃度の2/3乗に反比例して低下することとなる。従って、溶銑のAl濃度上昇の点からはAl灰を出来るだけ多量に添加した方が良い。1350℃におけるCaO,Al2 3 の活量を推定すると、図1のようになる。即ち、トリカルシウムアルミネート(3CaO・Al2 3 )の理論的Al2 3 濃度である37.7重量%まではaCaO は最大値1に保たれ、aAl2 O 3 の活量は最低値に留まっている。しかし、Al2 3 濃度が7%を超えるとaCaO が低下し、aAl2 O 3 が上昇する。この結果と(6)式より、Al灰混合比と平衡到達硫黄濃度の関係を求めると図2のようになる。ここでは、Al灰として表1の組成で示される産業廃棄物である低級グレードのAl灰の利用を考慮した。到達硫黄濃度が最低値となるAl灰混合比はトリカルシウムアルミネート(3CaO・Al2 3 )が生成する点である。従って、生石灰とAl灰の混合フラックス大の脱硫効率が得られるのは、CaOとAl灰中のAl2 3 の混合比率がモル比で3:1となる点であるという結論を得るに至った。
【0019】
【表1】
【0020】
次に、本発明者らは本理論を確認する試験を実施した。即ち、生石灰と表1の組成の産業廃棄物である低級グレードのAl灰を混合して溶銑の脱硫処理を行い、図3の結果を得た。生石灰とAl灰の重量混合比が約1:1で最大の脱硫率が得られることが明らかとなったが、この最適な組成は図2の結果で到達硫黄濃度が最低となる組成と良く一致した。
【0021】
この結果を基に、トーピードカーで生石灰とAl灰を事前に重量比で1:1に混合したフラックスを吹き込む試験を実施したが、低珪素溶銑の場合には溶銑側のAl濃度の増加とともにフラックスの脱硫効率K値が増加するという図4の結果を得た。
【0022】
更に、0.25%以上珪素を含む溶銑を本フラックスで脱硫処理したところ、Al濃度0.015%程度でAl添加の効果が飽和する傾向があり、低珪素濃度の場合と異なった。溶銑側に0.25%以上の珪素が溶解していると同一フラックスを用いてもあまり大きな脱硫効率改善効果は得られなかったが、これは生石灰表面に高融点のGehlenite(2CaO・SiO2 ・Al2 3 、融点:1600℃)が生成し、固体生石部への硫黄の拡散が妨げられるためである。
【0023】
本発明者らは、本発明に至る過程で反応機構に関する詳細な実験、検討を行った。すなわち、ロータリーキルンを用いて1000℃で石灰石を焼成して作成した塊状の生石灰を研磨し、直径約20mmの球形に成形したものを溶銑に浸漬し、120分間溶銑と反応させた後、生石灰を研磨して、生石灰断面の溶銑との接触面付近をX線マイクロアナライザーで分析した。
【0024】
図5は、反応初期の溶銑に珪素を0.5%、アルミニウムを0.07%、硫黄を0.05%含ませた場合のX線マイクロアナライザーによる観察結果である。この場合に、二次電子線像(SEM像)で、d1 ,d2 ,d3 ,d4 で示す位置の定量分析を実施した。その定量結果をCaO−SiO2 −Al2 3 三元系状態図上にプロットとして示す。極表面付近のd2 にはGehlenite(2CaO・Al2 3 ・SiO3 )の生成が認められた。また定性写真から、生石灰内部への硫黄、アルミニウムの浸透深さは10ミクロン程度しか生じていないことが明らかである。
【0025】
一方、図6は、反応初期に珪素を含まず、アルミニウムを0.021%含ませた溶銑に上記球形生石灰を120分間浸漬し、反応を行わせた後の生石灰断面の表面付近のX線マイクロアナライザー定性分析結果である。この場合には図5の結果に比べ、硫黄、アルミニウムの生石灰内部への浸透深さは大きく、かつ、硫黄も高濃度で濃化していることが明らかである。
【0026】
以上の結果を考察すると、珪素を含む溶銑の場合、反応の初期の段階で(5)式の反応のみならず(7)式の反応が併発し、CaO,Al2 3 とともにGehlenite(2CaO・Al2 3 ・SiO2 )を生成し、緻密な保護膜を形成するために硫黄、Alの生石灰内部への浸透を妨げているものと推察される。従って、図4で高珪素濃度溶銑の場合、Al濃度が0.02%までは脱硫効率が向上するものの、それ以上では多少アルミニウム濃度を高めても脱硫効率がさほど向上しなくなるのである。従って(5)式の脱硫反応をより有効に進めるためには、珪素濃度の低い条件が望ましく、本発明者らは、珪素濃度は0.25%以下が望ましいことを明らかとした。
2CaO(固体)+2S+Si=2CaS(固体)+SiO2 (固体)
‥‥(7)
【0027】
以上の検討結果をまとめれば、以下のような結論となる。
(イ)スラグ側の条件として、CaOとAl2 3 の混合比率は最大3CaO・Al2 3 の化学等量までAl2 3 を混合しても良いが、これ以上にな
ると、CaOの活量低下を招き、好ましくない。
(ロ)溶銑中にAl濃度は高い程脱硫効率を上げ得るが、珪素が0.25%以上存在すると、生石炭表面に高融点で緻密質のGehlenite を生成して生石灰
粒子内部への硫黄の浸透を防げ、好ましくない。
【0028】
工業的な応用を考慮すると、アルミニウム、Al2 3 のとしては産業廃棄物として多量に発生するAl灰が安価で利用価値が高いが、これを工業的に利用する手段として生石灰と混合して利用する本発明を開示したのである。また、産業廃棄物であるAl灰の品質のばらつき、即ち、Al2 3 含有率のばらつきを考慮すれば、CaOとAl2 3 のモル比率を厳密に3:1とすることはなかなか難しいが、本発明者らが行った試験によれば、Al2 3 に対するCaO重量比が1.65〜2.0の範囲であればほぼ同様な効果が得られることが明らかとなった。
【0029】
本法においては金属Al含有量が高いAl灰程、溶銑中のAl濃度が高くなり、脱硫効率は高くなるから、脱硫効率向上の上では望ましいが、一方で金属Al含有率が高いAl灰はAlの原料として価値があるため一般には高価であり、コスト面からは好ましくない。
【0030】
但し、金属Al含有率の高いAl灰が安価に入手可能であれば何等問題無く本法が適用できる。また、不純物としてSiO2 ,P2 5 ,B2 3 等脱硫作用を悪化させる作用のある酸性酸化物の濃度が高いものは好ましく無く、目安としてこれら酸性酸化物の濃度が総和で15%以下のAl灰を使用することが望ましい。また、フラックス中の金属Alの濃度が3%以下になってしまうと溶銑側のAl濃度があまり上昇しないので、脱硫効率は生石灰単味を使用した場合とあまり変わらなくなる。従って、フラックス中の金属Al含有率は3%以上とするのが望ましい。また、CaOとAl灰が予め焼成されたものであっても良い。
【0031】
なお、本発明法は上記のように固体状態での反応を基本とするため、脱硫剤の粒径が大きな塊状では反応が遅く、良い結果をもたらさないために微粉とするのが良く、目安として22mesh以下が望ましい。これより大きな粒径の場合、図7に示すように、Al灰を混合しても大して脱硫効率が向上しないからである。最も望ましくは微粉として溶銑中へ吹き込むのが良い。これが困難な場合には、溶銑上から高速のキャリアガスで搬送して吹き付ける、いわゆるブラスティング法も採用し得る。一方、あまり細かいと粉砕費用が過大となり、飛散してしまう等ハンドリング上の問題が生じること、吹き込み用のホッパー、ブロータンク、配管内への付着が起き、操業が不可能となる等の問題があり、微粉化には自ずと工業的に利用出来る限界があり、利用し得る範囲の粒径とすれば良いが、現在工業的に行われている範囲での微粉で十分である。
【0032】
更に、現在、高炉溶銑を原料とする多くの製鉄所では既に溶銑予備処理設備として脱珪処理あるいは脱りん処理設備を有しているので、これらの処理後溶銑を使えば、本発明法の高い脱硫効率が容易に得られることになる。また、珪素濃度0.25%以下の溶銑を原料としているような場合、本発明法を適用するだけの目的でこれらの予備処理を行うことは不必要である。また、反応容器としてはトーピードカー、溶銑鍋、誘導溶解炉などいずれでも良く、単に脱硫剤吹き込み装置とそれに付随する若干の設備追加等、従来の設備技術の範囲で十分実施し得るものである。
【0033】
【実施例】
(実施例1)
高炉溶銑291tをトーピードカーより溶銑予備処理炉にて脱珪脱りん処理を行った後、鍋に移し換え、生石灰52%、表2の組成のAl灰48%の比率で混合した脱硫ラックスを浸漬ランスを通じてN2 ガスをキャリアーとして吹き込み脱硫処理をった。脱硫剤の吹き込み速度は約150kg/minであった。処理前の珪素濃度は0.01%以下であり、処理前の溶銑温度は1290℃であった。15min 間の処理で溶銑中の硫黄濃度0.020%が0.002%に低下した。この時、溶銑の温度低下は約16℃であった。この時のCaO原単位は溶銑1tあたり4.0kg/t-pで脱硫反応のK値は0.50と高い値が得られた。ただし、K値は(8)式で示す、生石灰の利用効率を表す指標である。
K=ln([%S]i /[%S]f ) /WCaO ‥‥(8)
但し、[%S]i :処理前硫黄濃度(%)
[%S]f :処理後硫黄濃度(%)
WCaO :生石灰原単位(kg/t)
【0034】
【表2】
【0035】
(実施例2)
高炉溶銑287tを出銑樋でミルスケールなどの脱珪剤を投入して脱珪処理しつつトーピードカーへ移し換え、更に溶銑予備処理炉で脱りん処理を行った。その後、溶銑鍋に移し換えた後、上吹きランスを通じてN2 ガスをキャリアーガスとし生石灰33%、表3の組成のAl灰67%の比率で混合した脱硫フラックスのブラスティングによる脱硫処理を実施した。処理前の珪素濃度は0.10%であった。脱硫剤の供給速度は130kg/minであった。ノズル出口での線流速は350m/秒であった。15min 間の処理で溶銑中の硫黄濃度は0.022%から0.003%に低下した。この時、温度降下はわずか12℃であった。この時CaO原単位は2.24kg/tであり、K値として0.9という極めて高い値が得られた。
【0036】
【表3】
【0037】
(実施例3)
高炉溶銑160tをトーピードカーで受銑し、混入した高炉滓を除去した後、ミルスケール、酸素ガスを吹き込んで脱珪処理を行った。その後、脱珪滓を除滓した後、生石灰54%、表2の組成のAl灰46%の混合フラックスを吹き込み、脱硫処理行った。処理前の珪素濃度は0.17%であった。脱硫剤の供給速度は60kg/minであった。45min で硫黄濃度は0.019%から0.001%まで低下した。この時の溶銑の温度降下は25℃であった。生石灰原単位5.7kgでありK値として0.5という高い値が得られた。
【0038】
(比較例1)
高炉溶銑289tをトーピードカーより溶銑予備処理炉にて脱珪脱りん処理を行った後、鍋に移し換え、微粉の生石灰とソーダ灰混合脱硫剤を浸漬ランスを通じてN2 ガスをキャリアーとして吹き込み脱硫処理を行った。脱硫剤の生石灰とソー灰混合重量比は4:1であった。脱硫剤の吹き込み速度は約150kg/minであった。処理前の珪素濃度は0.1%以下であった。また処理前の溶銑温度は1305℃であった。30min 間の処理で溶銑中の硫黄濃度0.020%が0.003%に低下したに留まった。この時、溶銑の温度低下は約50℃と大きく、鍋への付着が発生した。ソーダ灰と生石灰を合わせた脱硫剤原単位は15.6kg/t、生石灰のみでも12.5kg/tと多量に要し、脱硫生石灰のK値は0.15と低い値しか得られなかった。
【0039】
(比較例2)
高炉溶銑289tをトーピードカーより受銑し、更に溶銑予備処理炉に移し換えて脱珪脱りん処理を行った。更に鍋に移し換え、微粉の生石灰を浸漬ランスを通じてN2 ガスをキャリアーとして吹き込み脱硫処理を行った。脱硫剤の粒度は200mh以下と超微粉を用いた。脱硫剤の吹き込み速度は約150kg/minであった。処理の溶銑温度は1307℃であった。30min 間の処理で溶銑中の硫黄濃度0.020%が0.00%に低下したに留まった。この時、溶銑の温度低下は約50℃と大きく、鍋への付着が発生した。また、K値は0.12と低かった。
【0040】
(比較例3)
高炉溶銑291tをトーピードカーにより受銑し、高炉スラグを除滓した後、生石灰31%、表3の組成のAl灰69%をN2 ガスをキャリアーガスとして浸漬ランスをて吹き込み、脱硫処理を行った。処理前の溶銑の珪素濃度は0.52%であった。脱硫剤の吹き込み速度は60kg/minであった。45min の処理で硫黄濃度は0.020%から0.011%まで低下したに留まった。K値は0.2に留まった。
【0041】
(比較例4)
高炉溶銑279tをトーピードカーより溶銑予備処理炉にて脱珪脱りん処理を行った後、鍋に移し換え、微粉の生石灰47%と表2の組成のAl灰53%より成る混合脱剤を浸漬ランスを通じてN2 ガスをキャリアーとして吹き込み脱硫処理を行った。脱硫剤の吹き込み速度は約150kg/minであった。処理前の珪素濃度は0.1%以下であった。また処理前の溶銑温度は1305℃であった。30min 間の処理で溶銑中の硫黄濃度0.020%が0.012%に低下したに留まり、目標の0.010%以下に低減出来なかった。この時、溶銑の温度低下は約25℃であった。脱硫生石灰のK値は0.17と低い値しか得られなかった。この原因は脱硫剤中のCaO/Al2 3 比が1.5と、最適範ある1.65〜2.0から低い方へ大きく逸脱していたためである。
【0042】
【発明の効果】
以上のように本発明によれば、従来の高価でかつ耐火物損耗の大きなCaF2 を含む生石灰系ラックス、あるいは耐火物損耗が大きく、温度低下の大きなソーダ灰系フラックスを使用せず、また産業廃棄物である低級グレードのAl残灰等の安価な原料を単に混合したのみの安価な脱硫剤を利用した効率の良い脱硫方法を提供する。これにより、安価なコストで0.001%以下の低硫黄濃度の溶銑が温度降下も少なく、容易に得られる。
このように、本発明は工業的規模において、容易かつ確実に、安価に極低硫黄鋼を溶製し得る脱硫剤を提供する。
【図面の簡単な説明】
【図1】1350℃におけるCaOとAl2 3 の混合体におけるAl2 3 重量濃度とCaO,Al量の関係を示す図。
【図2】CaOとAl灰混合脱硫剤のAl灰混合比と平衡到達硫黄濃度の関係を示す図。
【図3】本発明者らが本発明に至る試験で得られた生石灰とAl2 3 換算のAl灰混合比脱硫率の関係を示す図。
【図4】生石灰の脱硫効率K値と溶銑中Al濃度の関係を示す図。
【図5】Alを0.070%含み、珪素を0.50%含む溶銑と脱硫反応を行った生石灰粒子表面近傍の電子線マイクロアナライザー分析結果を示す図。
【図6】Alを0.021%含み、珪素を含まない溶銑と脱硫反応を行った生石灰粒子表面近傍の電子線マイクロアナライザー分析結果を示す図。
【図7】脱硫剤粒度と脱硫率の関係を示す図。
[0001]
[Industrial application fields]
The present invention relates to a high-efficiency desulfurization treatment method for hot metal, and is widely used in the hot metal pretreatment field.
[0002]
[Prior art]
Sulfur in steel has the property of deteriorating the properties of steel due to the formation of sulfide inclusions. For example, for steel pipes for sour, a sulfur concentration as low as 5 ppm is required.
[0003]
In order to meet these demands, desulfurization technology has been developed in steel refining. Of the desulfurization treatment, treatment at the hot metal stage uses lime, carbide, soda ash, etc. to produce sulfides such as CaS, Na 2 S, MgS, etc. using highly basic oxides or metallic Mg, etc., as slag A method of separating and removing is employed. Moreover, in order to achieve an extremely low sulfur concentration, desulfurization treatment of the coarsely refined molten steel using a CaO-based flux is also performed.
[0004]
In general, sulfur has a high binding force with alkali metals or alkaline earth metals such as Na, Mg, Ca, and the desulfurization treatment is to react with these elements as shown below to generate sulfides and remove them. . Among these, Na, Mg, and Ca have high binding strength in this order. However, as a material that can be supplied stably and inexpensively on an industrial scale, quick lime and limestone containing CaO as a main component, and Na 2 CO 3 as a main component. This is because soda ash, calcium carbide containing CaC 2 as a main component, or metal Mg is used. Among these, lime-based fluxes mainly composed of CaO are weaker than Na-based and Mg-based, but lime-based fluxes are rich in resources, are inexpensive and easy to handle. Widely used.
CaO + S → CaS + O (1)
Na 2 CO 3 + S → Na 2 S + CO 2 + O (2)
Mg + S → MgS (3)
[0005]
On the other hand, CaO itself has a very high melting point of 2800 ° C., and remains in a solid state even if it is simply brought into contact with molten iron. In this case, the desulfurization reaction proceeds by solid phase diffusion of S in solid CaO, but this process is generally known to be very slow. Accordingly, the solid CaO is poor in reactivity, so that the single substance has a drawback that the desulfurization rate is low. Therefore, ingenuity has been devised such as adding CaF 2 or the like and adding an auxiliary agent for increasing the hatching and melting properties and increasing the reactivity, or firing them beforehand to lower the melting point.
[0006]
On the other hand, the desulfurization process in the hot metal stage is lower in temperature than in the desulfurization process in the molten steel stage, and the reaction of the formula (1) tends to proceed to the right as the temperature is higher, which is disadvantageous compared to the process with molten steel. However, the addition of CaF 2 and other hatching aids has the advantage that the refractory wears significantly more in the molten steel stage, and there is an advantage due to the increased activity of sulfur in the molten iron due to the large amount of carbon contained in the molten iron. The hot metal desulfurization treatment is adopted.
[0007]
[Problems to be solved by the invention]
As the lime-based flux used in hot metal desulfurization, as described in Japanese Patent Publication Nos. 55-24925 and 63-195208, there is a description that CaO and Al 2 O 3 are mixed and melted with a specific composition. is there. Although these methods have an improvement effect on refining, pre-firing requires significant energy and deviates from the characteristics of quick lime-based flux, which is inexpensive because it leads to high flux costs. Although it is used in secondary refining for high-grade steels, it is a method that is not widely applicable to ordinary general steel.
[0008]
Japanese Patent Publication No. 2-305913 discloses that Al 2 O 3 is added to quick lime as a melting hatching aid and sprayed onto hot hot metal to melt the flux and promote the sulfur reaction. is there. In the case of the CaO—Al 2 O 3 binary system, it is known that the composition has the lowest melting point when the mixing ratio is 1: 1 by weight, and the melting point is about 1400 ° C. However, this method places restrictions on the temperature on the hot metal side. For example, there is a problem that it cannot be used at a temperature around 1350 ° C. after hot metal preliminary dephosphorization.
[0009]
Furthermore, Japanese Patent Publication No. 5-78723 has a description that SiO 2 or CaF 2 is mixed in order to improve the hatching meltability by the CaO—Al 2 O 3 system. Although SiO 2 is easy to use as an additive as a secondary material that can be obtained in large quantities at a low price in the form of silica or the like, it is preferable to use SiO 2 as a hatching aid because it reduces the desulfurization ability of slag. Absent.
Among the secondary materials that can be used industrially in steel refining, CaF 2 is known to best assist hatching of quicklime and does not reduce the desulfurization capacity of slag. Since it erodes significantly, for example, a mixed flux of CaO and CaF 2 is only used in secondary refining for some high-grade steels that require extremely low sulfur concentrations.
[0010]
On the other hand, it is well known that CaO is not completely hatched and melted but can be blown as fine powder to shorten the diffusion distance of S in solid quicklime and increase the desulfurization rate. Therefore, for example, Japanese Patent Publication No. 54-37020 discloses that the particle size of CaO blown into the hot metal is 0.4 mm or less. On the other hand, there are problems such as handling problems such as fine lime particle size scattering, sticking to the blowing hopper, blow tank, and piping, making operation impossible, etc. Naturally, there is a limit that can be industrially utilized.
[0011]
On the other hand, it is known that desulfurization efficiency is greatly affected by coexisting elements even when fine powder is blown.
For example, iron and steel vol. 61 (1975), p. 29, when the hot metal contains silicon, silicon is oxidized by free oxygen generated by the formula (1), and 3CaO.SiO 2 (melting point), which is a high melting point oxide on the surface of quicklime. : 2150 ° C.) and 2CaO.SiO 2 (melting point: 2180 ° C.) are formed, and it is known that the diffusion of S into quicklime particles is inhibited and the desulfurization rate is lowered. As a means for avoiding this, Japanese Patent Publication No. 56-23220 discloses that powder Al is blown into hot metal together with Al 2 O 3 and CaO to adjust the Al concentration in the hot metal in advance, and CaO and CaC 2 are further blown into the desulfurization. There is a statement to do so. There is a description that Al is added for the purpose of suppressing the oxidation reaction of silicon by oxygen, and the amount of Al added is defined by equation (4).
[% Al] = (0.01 to 0.1) [% Si] + (0.2 to 1.0) × Δ [% S] (4)
However, [% Si]: Silicon concentration in hot metal (wt%)
Δ [% S]: Target desulfurization width (% by weight)
[0012]
Further, Japanese Patent Publication No. 55-110711 discloses that Al is blown in the same manner as CaO from the viewpoint of suppressing oxidation of silicon.
With regard to this point, the inventors of the present invention have found that it is desirable to desulfurize with hot metal having a low silicon concentration when adding Al, and that very high desulfurization efficiency is obtained under such conditions. However, the hot metal having a high silicon concentration has a problem that the effect of the added Al cannot be maximized.
[0013]
As a similar technique, Japanese Patent Publication No. 56-58912 describes a desulfurization agent with calcium carbide 20 to 90%, quick lime 75 to 5%, and Al residual ash 1 to 5%. The rationale is ambiguous.
[0014]
Because of the problems as described above, the hot metal desulfurization process using lime-based flux is still widely practiced by blowing fine lime itself to the hot metal to some extent.
In view of such a situation, an object of the present invention is to provide a lime-based desulfurization agent that enables hot metal desulfurization treatment with high efficiency.
[0015]
[Means for Solving the Problems]
The present invention
(1) In the desulfurization treatment of hot metal using a mixed flux of quick lime as a main component and Al ash, the mixing ratio of CaO and Al 2 O 3 in the desulfurizing agent is 33 to 37.7% by weight in Al 2 O 3. Addition of quick lime and Al ash in an amount such that the mixing ratio of CaO and Al 2 O 3 after addition is within the range of 33 to 37.7 wt% in Al 2 O 3 A desulfurization method for low silicon concentration hot metal, which is characterized.
(2) The hot metal desulfurization agent according to (1), wherein a flux composed of a powder having a particle size of 22 mesh or less is blown.
[0016]
[Action]
When metal Al is present, the desulfurization reaction is represented by the following formula.
[0017]
3CaO (solid) + 3S + 2Al = 3CaS (solid) + Al 2 O 3 (solid) (5)
As the equilibrium reached sulfur concentration using an equilibrium constant of the reaction (6), the slag side CaO, Al 2 O 3, CaS of activity of aCaO, aAl 2 O 3, aCaS , the Al concentration in the molten iron It is expressed using.
Achieving equilibrium [% S] = {(aCaS aAl 2 O 3 ) / (KaCaO [% Al] 2 )} 1/3 (6)
[0018]
Since the slag is in a solid state at 1350 ° C. in this experimental condition, the reaction between the solid slag and the hot metal may be considered. That is, if the ratio is the same CaO—Al 2 O 3 , the equilibrium sulfur concentration decreases in inverse proportion to the 2/3 power of the Al concentration in the hot metal. Therefore, it is better to add as much Al ash as possible from the viewpoint of increasing the Al concentration of the hot metal. The activity of CaO and Al 2 O 3 at 1350 ° C. is estimated as shown in FIG. That is, up to 37.7% by weight, which is the theoretical Al 2 O 3 concentration of tricalcium aluminate (3CaO · Al 2 O 3 ), aCaO is kept at a maximum value of 1, and the activity of aAl 2 O 3 is at its lowest value. Stay on. However, when the Al 2 O 3 concentration exceeds 7%, aCaO decreases and aAl 2 O 3 increases. From this result and equation (6), the relationship between the Al ash mixing ratio and the equilibrium reached sulfur concentration is obtained as shown in FIG. Here, the use of low-grade Al ash, which is an industrial waste having the composition shown in Table 1, was considered as Al ash. The Al ash mixing ratio at which the reached sulfur concentration is the lowest is that tricalcium aluminate (3CaO · Al 2 O 3 ) is generated. Therefore, the conclusion that the desulfurization efficiency with a large mixed flux of quicklime and Al ash is obtained is that the mixing ratio of CaO and Al 2 O 3 in Al ash is 3: 1 in molar ratio. It was.
[0019]
[Table 1]
[0020]
Next, the present inventors conducted a test to confirm this theory. That is, hot lime and low-grade Al ash, which is industrial waste having the composition shown in Table 1, were mixed to desulfurize the hot metal, and the results shown in FIG. 3 were obtained. It became clear that the maximum desulfurization rate was obtained when the weight mixing ratio of quick lime and Al ash was about 1: 1, but this optimum composition is in good agreement with the composition with the lowest reached sulfur concentration in the results of FIG. did.
[0021]
Based on this result, a test was performed in which a flux in which quick lime and Al ash were mixed at a weight ratio of 1: 1 in advance was blown with a torpedo car. In the case of low silicon hot metal, the flux concentration increased with increasing Al concentration on the hot metal side. The result of FIG. 4 that the desulfurization efficiency K value increases was obtained.
[0022]
Furthermore, when hot metal containing 0.25% or more of silicon was desulfurized with this flux, the effect of Al addition tended to be saturated at an Al concentration of about 0.015%, which was different from the case of low silicon concentration. If 0.25% or more of silicon is dissolved on the hot metal side, even if the same flux is used, a great desulfurization efficiency improvement effect was not obtained, but this is because the high melting point Gehlenite (2CaO.SiO 2. This is because Al 2 O 3 (melting point: 1600 ° C.) is generated, and diffusion of sulfur to the solid raw stone portion is hindered.
[0023]
The present inventors conducted detailed experiments and examinations on the reaction mechanism in the process leading to the present invention. That is, a lump of quick lime prepared by firing limestone at 1000 ° C. using a rotary kiln is polished, and a spherical shape having a diameter of about 20 mm is immersed in hot metal and reacted with hot metal for 120 minutes, and then quick lime is polished. And the contact surface vicinity with the hot metal of a quicklime cross section was analyzed with the X-ray microanalyzer.
[0024]
FIG. 5 is a result of observation with an X-ray microanalyzer in the case where 0.5% of silicon, 0.07% of aluminum, and 0.05% of sulfur are contained in the hot metal at the initial stage of the reaction. In this case, a quantitative analysis was performed at positions indicated by d 1 , d 2 , d 3 , and d 4 in the secondary electron beam image (SEM image). The quantitative results are shown as a plot on the CaO—SiO 2 —Al 2 O 3 ternary phase diagram. Formation of Gehlenite (2CaO.Al 2 O 3 .SiO 3 ) was observed in d 2 near the pole surface. From the qualitative photographs, it is clear that the penetration depth of sulfur and aluminum into the quicklime is only about 10 microns.
[0025]
On the other hand, FIG. 6 shows an X-ray micrograph near the surface of the quicklime cross section after the spherical quicklime was immersed for 120 minutes in hot metal containing 0.021% aluminum and not containing silicon at the beginning of the reaction. It is an analyzer qualitative analysis result. In this case, it is clear that the penetration depth of sulfur and aluminum into quicklime is larger than that of FIG. 5 and that sulfur is also concentrated at a high concentration.
[0026]
Considering the above results, in the case of hot metal containing silicon, not only the reaction of the formula (5) but also the reaction of the formula (7) occurs at the initial stage of the reaction, and together with CaO and Al 2 O 3 , Gehlenite (2CaO · In order to form Al 2 O 3 .SiO 2 ) and form a dense protective film, it is presumed that the penetration of sulfur and Al into the quicklime is hindered. Therefore, in the case of the high silicon concentration hot metal in FIG. 4, the desulfurization efficiency is improved up to an Al concentration of 0.02%, but the desulfurization efficiency is not improved so much even if the aluminum concentration is increased more than that. Therefore, in order to advance the desulfurization reaction of the formula (5) more effectively, conditions with a low silicon concentration are desirable, and the present inventors have clarified that the silicon concentration is desirably 0.25% or less.
2CaO (solid) + 2S + Si = 2CaS (solid) + SiO 2 (solid)
(7)
[0027]
Summarizing the above results, the following conclusions can be drawn.
(B) as a condition of slag side, the mixing ratio of CaO and Al 2 O 3 may be mixed Al 2 O 3 up to stoichiometric maximum 3CaO · Al 2 O 3, but above which, the CaO The activity is reduced, which is not preferable.
(B) The higher the Al concentration in the hot metal, the higher the desulfurization efficiency. However, when silicon is present in an amount of 0.25% or more, high-melting and dense Gehlenite is formed on the raw coal surface, and sulfur inside the quick lime particles is generated. It prevents penetration and is not preferred.
[0028]
Considering industrial applications, aluminum and Al 2 O 3 are produced in large quantities as industrial waste, and as a result, they are inexpensive and have high utility value. The invention to be used has been disclosed. Further, variation in quality of the Al ash is industrial waste, i.e., considering the variation of the Al 2 O 3 content, CaO and Al 2 O 3 molar ratio strictly 3: It is very difficult to 1 However, according to the test conducted by the present inventors, it has been clarified that substantially the same effect can be obtained if the weight ratio of CaO to Al 2 O 3 is in the range of 1.65 to 2.0.
[0029]
In this method, Al ash with a higher metal Al content increases the Al concentration in the hot metal and increases the desulfurization efficiency, which is desirable for improving the desulfurization efficiency. On the other hand, Al ash with a high metal Al content is Since it is valuable as a raw material for Al, it is generally expensive and not preferable from the viewpoint of cost.
[0030]
However, this method can be applied without any problem as long as Al ash having a high metal Al content is available at low cost. Also, impurities having a high concentration of acidic oxides that have an effect of deteriorating the desulfurization action such as SiO 2 , P 2 O 5 , B 2 O 3 are not preferred as impurities, and as a guide, the concentration of these acidic oxides is 15% in total. It is desirable to use the following Al ash. Further, when the concentration of metal Al in the flux is 3% or less, the Al concentration on the hot metal side does not increase so much, so the desulfurization efficiency is not much different from the case of using quick lime. Therefore, the metal Al content in the flux is desirably 3% or more. Further, CaO and Al ash may be fired in advance.
[0031]
In addition, since the method of the present invention is based on the reaction in the solid state as described above, the reaction is slow when the particle size of the desulfurizing agent is large, and it is better to make fine powder in order not to give a good result. 22 mesh or less is desirable. In the case of a particle size larger than this, as shown in FIG. 7, even if Al ash is mixed, the desulfurization efficiency is not significantly improved. Most preferably, it should be blown into the hot metal as fine powder. If this is difficult, a so-called blasting method in which the steel sheet is transported and sprayed from the hot metal with a high-speed carrier gas may be employed. On the other hand, if it is too fine, the pulverization cost will be excessive, causing problems such as scattering, and problems such as the inability to operate due to adhesion to the blowing hopper, blow tank, and piping. There is a limit that can be industrially used for pulverization, and the particle size may be in a usable range. However, fine powder in the range that is currently industrially used is sufficient.
[0032]
Furthermore, at present, many steelworks using blast furnace hot metal as a raw material already have a desiliconization or dephosphorization equipment as a hot metal pretreatment equipment. Desulfurization efficiency can be easily obtained. Further, when hot metal having a silicon concentration of 0.25% or less is used as a raw material, it is unnecessary to perform these pretreatments for the purpose of applying the method of the present invention. The reaction vessel may be any of a torpedo car, a hot metal ladle, an induction melting furnace, etc., and can be sufficiently implemented within the scope of conventional equipment technology, such as simply adding a desulfurizing agent blowing device and a few equipment accompanying it.
[0033]
【Example】
(Example 1)
The blast furnace hot metal 291t was desiliconized and dephosphorized from a torpedo car in a hot metal pretreatment furnace, and then transferred to a pan, and desulfurized lux mixed with 52% quicklime and 48% Al ash with the composition shown in Table 2 was immersed in the lance. Through which N 2 gas was blown as a carrier for desulfurization treatment. The blowing rate of the desulfurizing agent was about 150 kg / min. The silicon concentration before the treatment was 0.01% or less, and the hot metal temperature before the treatment was 1290 ° C. In the treatment for 15 min, the sulfur concentration in hot metal 0.020% decreased to 0.002%. At this time, the temperature drop of the hot metal was about 16 ° C. At this time, the basic unit of CaO was 4.0 kg / tp / t of hot metal, and the K value of the desulfurization reaction was as high as 0.50. However, K value is a parameter | index showing the utilization efficiency of quicklime shown by (8) Formula.
K = ln ([% S] i / [% S] f ) / WCaO (8)
However, [% S] i : sulfur concentration before treatment (%)
[% S] f : Sulfur concentration after treatment (%)
WCaO: Quicklime basic unit (kg / t)
[0034]
[Table 2]
[0035]
(Example 2)
The blast furnace hot metal 287t was transferred to a torpedo car while adding a desiliconizing agent such as a mill scale at the output, and further dephosphorized in a hot metal pretreatment furnace. Then, after transferring to hot metal ladle, desulfurization treatment was performed by blasting desulfurization flux mixed with N 2 gas as carrier gas through a top blowing lance at a ratio of 33% quicklime and 67% Al ash with the composition shown in Table 3. . The silicon concentration before the treatment was 0.10%. The supply rate of the desulfurizing agent was 130 kg / min. The linear flow velocity at the nozzle outlet was 350 m / sec. The sulfur concentration in the hot metal decreased from 0.022% to 0.003% by the treatment for 15 minutes. At this time, the temperature drop was only 12 ° C. At this time, the CaO basic unit was 2.24 kg / t, and an extremely high value of 0.9 was obtained as the K value.
[0036]
[Table 3]
[0037]
(Example 3)
160 t of blast furnace hot metal was received with a torpedo car and mixed blast furnace iron was removed, and then desiliconization was performed by blowing mill scale and oxygen gas. Thereafter, after desiliconization, the mixed flux of 54% quick lime and 46% Al ash having the composition shown in Table 2 was blown to perform desulfurization treatment. The silicon concentration before the treatment was 0.17%. The supply rate of the desulfurizing agent was 60 kg / min. At 45 min, the sulfur concentration decreased from 0.019% to 0.001%. The temperature drop of the hot metal at this time was 25 ° C. The basic unit of quicklime was 5.7 kg, and a high K value of 0.5 was obtained.
[0038]
(Comparative Example 1)
289t of blast furnace hot metal was dephosphorized and dephosphorized in a hot metal pretreatment furnace from a torpedo car, then transferred to a pan, and desulfurized by blowing fine lime and soda ash mixed desulfurization agent through a dipping lance with N 2 gas as a carrier. went. The mixing weight ratio of quick lime and saw ash of the desulfurizing agent was 4: 1. The blowing rate of the desulfurizing agent was about 150 kg / min. The silicon concentration before the treatment was 0.1% or less. Moreover, the hot metal temperature before a process was 1305 degreeC. In the treatment for 30 min, the sulfur concentration in the hot metal 0.020% only decreased to 0.003%. At this time, the temperature drop of the hot metal was as large as about 50 ° C., and adhesion to the pan occurred. The unit of desulfurization agent combined with soda ash and quick lime was 15.6 kg / t, and quick lime alone required a large amount of 12.5 kg / t, and the K value of desulfurized quick lime was as low as 0.15.
[0039]
(Comparative Example 2)
The blast furnace hot metal 289t was received from a torpedo car, and further transferred to a hot metal pretreatment furnace for desiliconization and dephosphorization. Further, it was transferred to a pan, and desulfurization treatment was performed by blowing fine quicklime through a dipping lance using N 2 gas as a carrier. The particle size of the desulfurizing agent was 200 mh or less and ultrafine powder was used. The blowing rate of the desulfurizing agent was about 150 kg / min. The hot metal temperature for the treatment was 1307 ° C. In the treatment for 30 min, the sulfur concentration in the hot metal 0.020% only decreased to 0.00%. At this time, the temperature drop of the hot metal was as large as about 50 ° C., and adhesion to the pan occurred. The K value was as low as 0.12.
[0040]
(Comparative Example 3)
After receiving the blast furnace hot metal 291t with a torpedo car and removing the blast furnace slag, 31% quick lime and 69% Al ash having the composition shown in Table 3 were blown with a dipping lance using N 2 gas as a carrier gas and subjected to desulfurization treatment. . The silicon concentration of the hot metal before the treatment was 0.52%. The blowing speed of the desulfurizing agent was 60 kg / min. With the 45 min treatment, the sulfur concentration only dropped from 0.020% to 0.011%. The K value remained at 0.2.
[0041]
(Comparative Example 4)
The blast furnace hot metal 279t was dephosphorized and dephosphorized from a torpedo car in a hot metal pretreatment furnace, and then transferred to a pan, where a mixed desiccant composed of 47% fine lime and 53% Al ash with the composition shown in Table 2 was immersed Through which N 2 gas was blown as a carrier for desulfurization treatment. The blowing rate of the desulfurizing agent was about 150 kg / min. The silicon concentration before the treatment was 0.1% or less. Moreover, the hot metal temperature before a process was 1305 degreeC. In the treatment for 30 minutes, the sulfur concentration in the hot metal 0.020% only decreased to 0.012%, and could not be reduced to the target of 0.010% or less. At this time, the temperature drop of the hot metal was about 25 ° C. The K value of desulfurized quicklime was only as low as 0.17. This is because the CaO / Al 2 O 3 ratio in the desulfurizing agent is 1.5, which is greatly deviated from the optimum range of 1.65 to 2.0, which is lower.
[0042]
【The invention's effect】
As described above, according to the present invention, conventional lime-based lux containing CaF 2 which is expensive and has a large refractory wear, or a soda ash flux having a large refractory wear and a large temperature drop is not used. Provided is an efficient desulfurization method using an inexpensive desulfurization agent obtained by simply mixing inexpensive raw materials such as low-grade Al residual ash as waste. As a result, a hot metal having a low sulfur concentration of 0.001% or less can be easily obtained at a low cost with little temperature drop.
As described above, the present invention provides a desulfurization agent capable of melting ultra-low sulfur steel easily and reliably on an industrial scale at low cost.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the weight concentration of Al 2 O 3 and the amount of CaO and Al in a mixture of CaO and Al 2 O 3 at 1350 ° C.
FIG. 2 is a graph showing a relationship between an Al ash mixing ratio of CaO and an Al ash mixed desulfurization agent and an equilibrium reached sulfur concentration.
FIG. 3 is a graph showing the relationship between quick lime obtained in the test leading to the present invention and Al ash mixing ratio desulfurization rate in terms of Al 2 O 3 .
FIG. 4 is a graph showing the relationship between quick lime desulfurization efficiency K value and Al concentration in hot metal.
FIG. 5 is a diagram showing an electron beam microanalyzer analysis result in the vicinity of the surface of quicklime particles obtained by desulfurization reaction with hot metal containing 0.070% Al and 0.50% silicon.
FIG. 6 is a diagram showing the result of electron beam microanalyzer analysis in the vicinity of the surface of quicklime particles obtained by performing desulfurization reaction with hot metal containing 0.021% Al and not containing silicon.
FIG. 7 is a graph showing the relationship between the desulfurization agent particle size and the desulfurization rate.

Claims (2)

生石灰を主成分とするフラックスとAl灰の混合フラックスによる溶銑の脱硫処理に際し、脱硫剤中のCaOとAl2 3 の混合比がAl2 3 で33〜37.7重量%の範囲となるように混合したもの、または添加後のCaOとAl2 3 の混合比がAl2 3 で33〜37.7重量%の範囲となる量の生石灰、Al灰を添加することを特徴とする低珪素濃度溶銑の脱硫方法。In the desulfurization treatment of hot metal using a mixed flux of quick lime as a main component and Al ash, the mixing ratio of CaO and Al 2 O 3 in the desulfurizing agent is in the range of 33 to 37.7 wt% with Al 2 O 3. Or a mixture of CaO and Al 2 O 3 after the addition is added in an amount of 33 to 37.7% by weight with Al 2 O 3 , quick lime and Al ash are added. Desulfurization method of low silicon concentration hot metal. 原料の粒度が22mesh以下の粉体から成るフラックスを吹き込む請求項1記載の溶銑の脱硫剤。The hot metal desulfurization agent according to claim 1, wherein a flux composed of a powder having a particle size of 22 mesh or less is blown.
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